1. Field of the Invention
The present invention relates to a film formation method and a film formation apparatus for forming a zirconia-based film on a substrate to be processed, such as a semiconductor wafer or the like.
2. Description of the Related Art
Recently, as an LSI is required to be more highly integrated and operate faster, a design rule for a semiconductor device constituting the LSI is more complicated. Accordingly, a dielectric film is required to have a higher capacity, and to have a lower EOT (Equivalent Oxide Thickness), which refers to a thickness of a dielectric film scaled by a ratio of a dielectric constant of the dielectric film to a dielectric constant of SiO2, and a higher dielectric constant. In order to have a higher dielectric constant, a dielectric film needs to be crystallized. Furthermore, a film is required to have a higher crystallinity. Also, according to each of devices, since there is a limitation of thermal budget, a film is required to be formed or crystallized at a low temperature.
As a high dielectric constant material meeting these requirements, a zirconium oxide (ZrO2) film is examined (for example, in Patent Reference 1). Also, as a method of forming a zirconium oxide film at a low temperature, an ALD process that uses, for example, tetrakis(ethylmethylamino)zirconium (TEMAZ) as a material gas (precursor) and for example, an O3 gas as an oxidizing agent, and alternately supplies the material gas and the oxidizing agent is known (for example, in Patent Reference 2). Since zirconium oxide is easily crystallized, zirconium oxide may be crystallized without adversely affecting a device by being formed at a low temperature in such a method or then being annealed at a temperature of 450° C. or lower.
However, although such a dielectric film is required to have a high dielectric constant and a small leakage current, once the dielectric film is crystallized as described above, a leakage current is increased due to a crystal grain boundary leakage in which current leaks from a crystal grain boundary.
In order to solve the problem, there is suggested in Patent Reference 3a method including a process of forming a ZrO2 film on a substrate by alternately supplying a zirconium material and an oxidizing agent into a process chamber for a plurality of times and a process of forming a SiO2 film on the substrate by alternately supplying a silicon material and an oxidizing agent once or for a plurality of times. According to the method, the processes are performed by adjusting the number of times the materials and the oxidizing agent are supplied, such that a Si concentration in the film ranges from 1 to 4 atm %, the ZrO2 film formation and the SiO2 film formation based on the adjusted number of times are treated as a single cycle, and the cycle is performed once or for a plurality of times to form a zirconia-based film having a predetermined film thickness. Accordingly, since a grain boundary leakage is suppressed with maintaining a zirconia crystal, the method can achieve a small leakage current with maintaining a high dielectric constant equal to that of a ZrO2 single film.
3. Prior Art Reference
(Patent Reference 1) Japanese Patent Laid-Open Publication No. 2001-152339
(Patent Reference 2) Japanese Patent Laid-Open Publication No. 2006-310754
(Patent Reference 3) Japanese Patent Laid-Open Publication No. 2010-067958